C# Java. C# Types Naming Conventions. Distribution and Integration Technologies. C# C++.NET A C# program is a collection of: C C++ C# Language

Transcription

1 C# Java Distribution and Integration Technologies C# Language C C++ C# C++.NET A C# program is a collection of: Classes Structs Interfaces Delegates Enums (can be grouped in namespaces) One entry point (static int Main(string[ ] args)) Some aspects of the C# Language 2 CTS type intrinsic C# type (defined by a keyword) System.SByte sbyte (8 bits) System.Byte byte (8 bits) System.Int16 short (16 bits) System.UInt16 ushort (16 bits) System.Int32 int (32 bits) System.UInt32 uint (32 bits) System.Int64 long (64 bits) System.UInt64 ulong (64 bits) System.Char char (unicode) System.Single float (32 bits) System.Double double (64 bits) System.Boolean bool (true/false) System.Decimal decimal (128 bits - fixed point) System.Object object System.String string System.Array [ ] C# Types Naming Conventions Casing Words are capitalized (z.b. ShowDialog) First letter in upper case, except for local variables, private fields and constants constants upper case SIZE, MAX_VALUE local variables lower case i, top, sum private fields lower case data, lastelement public fields upper case Width, BufferLength properties upper case Length, FullName enumeration constants upper case Red, Blue methods upper case Add, IndexOf types upper case StringBuilder (predefined types in lower case: int, string) namespaces upper case System, Collections First word Names of void methods should start with a verb (e.g. GetHashCode) Other names should start with a noun (e.g. size, IndexOf, Collections) Enumeration constants or bool members may start with an adjective (Red, Empty) Some aspects of the C# Language 3 Some aspects of the C# Language 4

2 Operators and Statements Operators: Same as C/C++ plus some others: typeof(obj or type) (representation as Type), is (tests a type), as (cast or null) Statements: assignment; expression; if (bool_exp) { [ else { ] switch (expr) switch_block while (bool_expr) { do { while (bool_expr); for (init; cond; iter) { foreach (var in expr) { break; continue; throw [ expr ]; return [ expr ]; try { catch [ ( exception ) ] { finally { lock (obj) { using ( res_expr ) { Some aspects of the C# Language 5 C# Classes Each class can have: Fields and Constants (const and readonly) Methods + constructors (instance and type) Finalizers Properties and indexers Events Operators and converters Nested types Other class characteristics Simple inheritance (but multiple interfaces) Values can be treated as objects Much more Some aspects of the C# Language 6 Example C# - Value as an object Boxing and unboxing i o j 123? int i = 123; object o = i; int j = (int) o; System.Int32 Boxing Unboxing struct Point { public int x, y; class App { static void Main( ) { ArrayList a = new ArrayList( ); Point p; for (int k = 0; k < 10; k++) { p.x = p.y = 1; automatic boxing a.add(p); explicit unboxing Point p1 = (Point) a[4]; public virtual void Add(object o); class App { static void Main( ) { Point p; p.x = 10; p.y = 20 ; Console.WriteLine(p.ToString()); Console.WriteLine(p.GetType()); Point p2 = (Point) p.clone(); ICloneable c = p2; object o = c.clone(); p = (Point) o; Another example Some aspects of the C# Language 7 Some aspects of the C# Language 8

3 C# Modifiers Type attributes abstract sealed Finalizers Execute before the destruction of objects by the garbage collector It is a non deterministic execution Don t have any modifiers Accessibility for types, fields and methods private (default for methods, fields) protected internal (default for non-nested) protected internal (or) public (protected and internal) (not supported in C#) Method attributes (none) - static virtual new override abstract Field attributes instance class Test { ~Test( ) { // finalization work // automatically calls the base class // finalizer (none) - static const readonly instance Some aspects of the C# Language 9 Some aspects of the C# Language 10 Properties Smart Fields (methods used with a field syntax) Usage: class Data { FileStream s; public string FileName { set { s = new FileStream(value, FileMode.Create); get { return s.name; Data d = new Data(); d.filename = myfile.txt ; string name = d.filename; For a property that is simply a getter and/or a setter of a private field we don t need to write the code: public int SomeValue { get; set; Indexers methods that are used as an array element syntax Usage: File f = int x = f[10]; f[11] = (int) A ; class File { FileStream s; public int this [int index] { get { s.seek(index, SeekOrigin.Begin); return s.readbyte(); set { s.seek(index, SeekOrigin.Begin); s.writebyte( (byte)value ); It s possible to define several indexers with different index types Some aspects of the C# Language 11 Some aspects of the C# Language 12

4 Nested types It s possible to define types inside types (usually classes) class A { int x; B b = new B(this); public void f() { b.f(); public class B{ A a; public B(A a) { this.a = a; public void f() { a.x= ; a.f(); class C { A a = new A(); A.B b = new A.B(a); Internal classes can access any member from the external one (even private) External classes can only access public members of the internal classes Other classes can access the internal classes only if they are public Structures, enumerations, interfaces and delegates can also be nested Generics Type parameters applied to classes, interfaces, methods, events or delegates public class MyStack<T> { T[] items = null; int top = 0; public MyStack(int capacity) { items = new T[capacity]; public void Push(T item) { public T Pop() { MyStack<double> astack = new MyStack<double>(100); Some aspects of the C# Language 13 Some aspects of the C# Language 14 Delegates (1) A delegate is a type representing a method (a smart, verifiable, method pointer type) They can be instantiated with any method corresponding to the declared signature When invoked executes the method used to instantiate it Declaration: delegate void Notifier( string sender ); Variable: Notifier greetings; Instantiation: void SayHello(string sender) { Console.WriteLine("Hello from " + sender); Usage: greetings( Mike ); greetings = new Notifier(SayHello); or greetings = SayHello; // invokes SayHello( Mike ) Equal to the declaration of a method, but adding the delegate keyword Delegates (2) The delegates are multicast: this means that they can contain several methods (they must have all the same signature) In this case, when invoked, they execute all the included methods Notifier greetings; greetings = SayHello; greetings += SayGoodBye; greetings("john"); // "Hello from John // "Good bye from John greetings -= SayHello; greetings( Mike"); // "Good bye from Mike" When a delegate returns a value and is multicast, only the value from the last call is returned (the same for out parameters) Some aspects of the C# Language 15 Some aspects of the C# Language 16

5 Anonymous Methods When needing or instantiating a delegate we can use anonymous methods: Some examples: Lambdas Simple forms to express anonymous methods used to instantiate delegates (input parameters) => expression delegate void SomeDel(int x); SomeDel adel = delegate(int k) { k // explicit delegate initialization (x, y) => x == y (int x, string s) => s.length > x () => SomeMethod() x => x * x // delegate method parameter void CreateAThread() { Thread t1 = new Thread(delegate() { ); t1.start(); (input parameters) => { statements n => { string s = n + " " + "World"; Console.WriteLine(s); button1.click += delegate(object sender, EventArgs e) { MessageBox.Show( Button pressed! ); // event handler Lambdas can be asynchronous if declared so async (input parameters) => { statements Some aspects of the C# Language 17 Some aspects of the C# Language 18 Events (1) An event is a member (variable) belonging to a special delegate type (keyword event) Can be subscribed by other classes Only the class that declares the event can fire it (invoke) class Model { public event Notifier notifyviews; public void Change() { notifyviews("model"); // fire the event class View { public View(Model m) { m.notifyviews += Update; // subscribe the event void Update(string sender) { Console.WriteLine(sender + " was changed"); class Test { static void Main() { Model m = new Model(); new View(m); m.change(); Some aspects of the C# Language 19 Events (2) delegate void handler( ); public class event_gen { public event handler ev; void method( ) { if ( ) if (ev!= null) ev( ); // fire the event public class use_event { use_event( ) { event_gen evg = new event_gen( ); evg.ev += new handler(ev_hdlr); // register a listener void ev_hdlr( ) { Some aspects of the C# Language 20

6 Asynchronous Calls (1) The CLR allows that any method from any class or struct (including remote ones) could be invoked asynchronously. A new thread is automatically Synchronous Call created to execute the call. Synchronous call call Callee Asynchronous call async call wait for result caller and callee run in parallel Callee return result Asynchronous Calls (2) Classical code in C# (using a delegate) We only need to create a delegate instantiated with the method to call, and invoke the BeginInvoke( ) method from the delegate instance delegate name ( ); AsyncCallback cb = new AsyncCallback(Handler) name del = new name ( f ); IAsyncResult ar = del.begininvoke( params, ); ar.iscompleted v = del.endinvoke(ar); EndInvoke() collects the call result void Handler(IAsyncResult ar) { v = del.endinvoke(ar); Demo Sieve Some aspects of the C# Language 21 Some aspects of the C# Language 22 Asynchronous Calls (3) A recent version of C# (5.0) introduced the keywords async and await Can be used with the Task.NET class async marks methods that have asynchronous calls inside them await make an immediate return, and continues execution after the call completes the call can be a Task.Run or other async method async void MethodAsync(int par) { // preparation int res = await Task.Run<int>( () => MyTask(par) ); // do something with res - completion int MyTask(int par) { // some code MethodAsync(1000); async methods can return: void, Task or Task<T> Task has the property IsCompleted to test in the caller if the async method has already executed to completion Task<T> has the property Result. Getting it waits for completion. Keywords async and await async void FooAsync() { Task<int> task = CalcAsync(); int result = await task; FooAsync(); Task<int> CalcAsync() { return Task.Run(() => {); FooAsync() task = CalcAsync(); CalcAsync() result = await task; If a method contains await it must be marked as async and should have the suffix Async task and section run in parallel meaning of await: - if task ready => get its result and continue with - if not ready => return to caller and continue there; execute ("continuation") when task gets ready FooAsync(); FooAsync() task = CalcAsync(); CalcAsync() result = await task; "continuation" threads marked by different colors Some aspects of the C# Language 23 Some aspects of the C# Language 24

7 Accessing native code Invoking native code from native dynamic libraries (DLL s) is very simple. The native functions run in the same application domain that calls them. We need only to declare the functions using the static extern modifiers, inside some class or struct class something { [DllImport( some.dll )] static extern int some_func(char ch, double d); void method( ) { v = some_func( b, 14.21); Simple types are transformed correctly by default. For more complex types we can use some.net attributes to guide their transformation and memory layout (for instance in structs) Some aspects of the C# Language 25 Framework Class Library (FCL) Int32, String, UI Web Data System Windows EnterpriseServices XML Runtime Services Forms XmlDocument, ServicedComponent, Remoting Connection, DataSet, FCL evolution Organized in nested namespaces System is the base Some aspects of the C# Language 26